<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    .box1 {
        width: 200px;
        height: 200px;
        background-color: #bfa;
        /* float: left; */
        overflow: hidden;
    }

    .box2 {
        width: 200px;
        height: 200px;
        background-color: orange;
        overflow: hidden;
        /* 不被浮动的元素覆盖 */
        /* 无论什么方法开启bfc 就具备那几个特点 */
    }

    .box3 {
        width: 100px;
        height: 100px;
        background-color: yellow;
        margin-top: 100px;
    }
</style>


<body>
    <div class="box1">
        <div class="box3"></div>
    </div>
    <!-- <div class="box2"></div> -->

</body>

</html>